Not sure if I've remembered correctly, but I believe that back when Totalbiscuit was covering things related to WoW, he pointed out that the transfer fee was no longer justifiable because the adminstrative processes had been simplified.

Now consider Classic WoW, Burning Crusade, and WotLK. Blizzard has almost certainly sold enough copies of those that they recouped their development costs, right? So, why not have Classic WoW and the first two expansions be completely free?

I'm pretty sure the costs of those expansions have gone down significantly and that at least one of the expansions is now completely free.